Rotor constructions in gas turbine engines can include a plurality of blade carrying rotor disks separated by annular disk spacer arms. U.S. Pat. No. 3,647,313, assigned to the General Electric Company, discloses a compressor rotor structure with disks separated by annular spacer arms, and a system for cooling the rotor construction. It is desirable to minimize the amount of cooling air used to cool rotors and spacer arms in order to increase engine cycle efficiency.
U.S. Pat. No. 3,056,579, assigned to the General Electric Company, discloses a composite disk structure having a first catenary-shaped portion performing a heat shield function, and a second axially aligned stiffening member, which can have a cylindrical spacer form. Cooling fins are shown positioned on the catenary heat shield. However, the finned heat shield of U.S. Pat. No. 3,056,579 can introduce performance penalties in practice. Centrifugal loads as well as heat and pressure induced loads generated in the catenary shield are transferred to the disk rims (as discussed in Col. 3, line 63-66). This load transfer to the disk rim is due to the fact that the catenary shield is, by design, not a self supporting wheel structure capable of carrying its own centrifugally induced loads. Therefore, the added centrifugal loads due to the added weight of the fins on the catenary shield increase the disk rim stress by increasing the centrifugal load transmitted to the disk rims. Thus, the added fins on a structure which is not a self-supporting wheel structure can require extra cooling air or disk rim material to maintain disk rim stresses at an allowable level for a given operating temperature. The added weight of the fins will also increase the hoop stress in the catenary shield.
Further, fins positioned on the heat shield do not effectively reduce thermal distortions in the structural disk spacer arm, and the resultant stresses in the spacer arm and adjacent disks. Temperature gradients in the disk spacer arms distort disk spacer arms and can result in detrimental bending stresses in the spacer arms and adjacent disk rims where the spacer arms transmit bending loads between adjacent disks, especially during transient operating conditions where the spacer arms respond to temperature changes more quickly then adjacent disks or connecting flanges.
Additionally, gas turbine engineers seek to increase turbine operating temperatures for improved engine efficiency, while maintaining turbine component temperatures within allowable limits with a minimal amount of cooling air.